Theoretically, in a measurement tool, electrodes connected by an electrically conductive wire in the tool should have same potential with respect to a reference electrode. However the wire connection between the electrodes usually has a non-negligible resistance. As a result, when a current passes through the wire it can produce a considerable voltage differential between the electrodes. This effect can introduce errors in evaluation of a data from a measurement tool. This can be most pronounced when a resistance based measurement tool moves between regions under measurement having a high resistivity contrast. For example, using an array laterolog tool in a measurement of resistivity of the formation around a borehole in a drilling operation, when the array laterolog tool moves across a layer boundary with high formation resistivity contrast, high currents can be induced across wires used to balance electrode pairs in the array laterolog tool to a common voltage. This unaccounted effect may produce inaccuracies in the measurement of apparent resistivity of the formation.
An array laterolog is a current based tool in which a current is generated from the tool and resistivity is determined from measured voltages based on Ohm's law. The array laterolog typically includes a central current electrode with additional current electrodes above and below the central current electrode, where the additional current electrodes are used to achieve focusing, and monitor electrodes to measure the signals that go into the evaluation of resistivity. Typically, the additional current electrodes can be arranged to force flow perpendicular to the axis of the logging device in a lateral direction. The current electrodes and monitor electrodes can be arranged in pairs. However induced currents as discussed above may prevent the setting and keeping of selected electrodes to the same potential. As a result, the usefulness of such measurements in providing precision or quality information derived from such measurements can be affected the resistances in wires intended to balance electrodes of the array laterolog tool.